1. Technical Field
The present invention relates to control supply of fuel gas, and more particularly to a method for controlling fuel gas flow to a gas-fired appliance during power surges or outages.
2. Description of Related Art
A gas-fired appliance heats objects with flame generated by burning combustible gas. A traditional gas-fired appliance comprises a combustor and a manual regulating valve, wherein the combustor burns fuel gas, and the manual regulating valve can be used to manually adjust the flow of fuel gas supplied to the combustor. For precise flow control, an advanced gas-fired appliance uses a proportional valve instead of the manual regulating valve to control the flow. Particularly, the flow of the fuel gas is precisely controlled by adjusting the current passing through the coil of the proportional valve.
While such a proportional valve may provide precise flow control, it requires continuous power supply to the coil even for constant flow output only, which increases power consumption. For this problem, a solution has been proposed that uses a motor-controlled flow-regulating valve together with a solenoid valve to replace the foregoing proportional valve, wherein a controller controls the motor of the flow-regulating valve to drive a valve plug to close the valve opening of the flow-regulating valve as required, so as to change the flow, and the solenoid valve serves to allow or disallow the fuel gas to pass the valve. Whereby, after the fuel gas output by the flow-regulating valve is adjusted to a desired flow, even if the motor is unpowered, the constant flow can still be maintained. In addition, since the solenoid valve consumes less power than the proportional valve does, the benefit of saving energy can be achieved.
When the power supplied to the gas-fired appliance is cut off, the controller loses the power and is not able to control the motor, so the valve opening of the flow-regulating valve remains open. At this time, the solenoid valve stops the fuel gas, so as to prevent more supply of the fuel gas to the combustor. However, after power restoration, the controller has no way to know how much the valve opening of the flow-regulating valve is open, which increases the difficulty of subsequent control. In addition, after power restoration, the fuel gas will immediately arrive at the combustor as soon as the solenoid valve is open, and may dangerously leak out if the fire is not immediately ignited.